2. Field of the Invention
This invention relates generally to the disposal of municipal and industrial waste materials by combustion, in the presence of at least 50% oxygen and more particularly, to a process for waste combustion process which does not require separation of non-ferrous metals from the bulk waste material and which is adapted to simultaneously treat various combinations of the same.
2. Description of the Prior Art
In industries, households, and during the recycling of secondary substances, waste materials are produced which have a relatively high calorific value and which therefore present an opportunity to reduce the volume of waste by combustion. Such a reduction in the volume of waste would be desirable in order to prevent ground water contamination and to conserve landfill space. Processes for the combustion of municipal solid waste and other refuse using air are well known and need not be described here. A process for the incineration of combustible material, including municipal waste, in which the combustion air has an increased oxygen content, is described in published European Application EP-A 0207924. In that publication, the preferred oxygen content is 30-35% by weight, compared with the 23.19% by weight oxygen content of atmospheric air.
European Publication EP-A 0103881 deals with a process for the elimination of hazardous gaseous flue gas components. In that process, a cleaning is step is proposed in which lime or calcium carbonate is introduced into the flue gas downstream of the combustion furnace. For the same purpose, WO 86/07602 discloses that powdery additives of dicalcium-phosphate and ammonium chloride, with small contents of other chemicals, may be introduced into the combustion process. The WO/86/07602 reference, however, does not mention suitable ranges of temperatures.
In European Publication EP-A 0023642, there is proposed a mixture of red-slime with alkaline earth and aluminum hydroxide as adsorption matter. This mixture is introduced into a stream of waste gases at a temperature of approximately 300.degree. C.
In British Publication GB-A 2,169,887, a process is disclosed in which pulverized alkali- or alkaline earth- oxides or carbonates thereof are blown into a combustion furnace at 800.degree.-1000.degree. C. Water or steam is separately injected into the flue gas.
In all combustion processes, waste gases occur which contain hazardous dust and also hazardous gaseous components. For example, hydrochloric acid arises from the combustion of polyvinyl chloride. Moreover, in bunting chlorinated or fluorinated hydrocarbons, dangerous chemical compounds can occur if special conditions of combustion are not observed and maintained.
For combustion with air, a greater amount of excess air is generally necessary for complete combustion to occur. Moreover, an after burning is essential for complete combustion because of the low temperature in the primary combustion chamber. Because the after burner needs additional fuel, the amount of waste gas is consequently increased. Accordingly, the heat recovery and gas cleaning installations are large and expensive. Additionally, although the concentration of pollutants in the cleaned gas is low, the overall emission level of hazardous substances is high because of the large volume of the gas stream.
It has already been proposed to improve the combustion by utilizing oxygen enriched air, for example, in the combustion of combustible residues from automobile shredders (Wilhelm C. Dries--Recycling Berlin 1979, S. 1447). A drastic reduction in the amount of waste gases occurs only if the combustion air contains at least 50% oxygen, but best results are obtained if pure oxygen with 99% O.sub.2 is used for the combustion.
The magnitude of the reduction in the amount of waste gases is illustrated by the combustion of 1 kg of light oil. With an excess air value of 1.2, about 13 Nm.sup.3 of flue gas is produced when the oil is combusted. In contrast, combustion of the same oil in pure oxygen produces only 3.2 Nm.sup.3 of flue gas, a 75% reduction. Accordingly, the size and power consumption of the gas clean unit are substantially reduced.
A process for treatment of scrap batteries, as described in published German Patent Application P 36 17410.6, has been utilized for a long time. In that publication, it is disclosed that a complete and sootfree combustion of the plastic parts of batteries, as propylene and polyvinyl chloride, may be obtained if the materials are retained in the combustion furnace for a predetermined retention time.
Each of the aforementioned processes is limited in that it is adapted to treat only a portion of the components which are present in the overall waste stream.